Normal functioning of the immune system is crucial to the health of man, and diet is one of the major exogenous factors modulating individual immunocompetence. Recently, nutrition research has focused on the role of foods or specific food components in enhancing immune system responsiveness to challenges and thereby improving health and reducing disease risks. Assessing diet-induced changes of immune function, however, requires a thorough methodological approach targeting a large spectrum of immune system parameters. Currently, no single marker is available to predict the outcome of a dietary intervention on the resistance to infection or to other immune system-related diseases. The present review summarises the immune function assays commonly used as markers in human intervention studies and evaluates their biological relevance (e.g. known correlation with clinically relevant endpoints), sensitivity (e.g. within-and between-subject variation), and practical feasibility. Based on these criteria markers were classified into three categories with high, medium or low suitability. Vaccine-specific serum antibody production, delayed-type hypersensitivity response, vaccine-specific or total secretory IgA in saliva and the response to attenuated pathogens, were classified as markers with high suitability. Markers with medium suitability include natural killer cell cytotoxicity, oxidative burst of phagocytes, lymphocyte proliferation and the cytokine pattern produced by activated immune cells. Since no single marker allows conclusions to be drawn about the modulation of the whole immune system, except for the clinical outcome of infection itself, combining markers with high and medium suitability is currently the best approach to measure immunomodulation in human nutrition intervention studies. It would be valuable to include several immune markers in addition to clinical outcome in future clinical trials in this area, as there is too little evidence that correlates markers with global health improvement.Immune function: Marker: Diet: Human studies: Infections
Task and objectivesThe major function of the immune system is to protect the body against infectious diseases. The immune system can be divided into innate and adaptive immunity. The immune system operates at the systemic as well as at the local level, which includes the mucosal tissue such as in the upper airways and the gut. A fundamental characteristic of the immune system is that it involves multiple, functionally differing cell types, which permit a large variety of defence mechanisms. Assessing the status of the immune system and its functionality therefore requires a thorough methodological approach targeting a large spectrum of immune †A draft version of this review was extensively discussed with experts from the fields of nutrition, (clinical) immunology, mucosal immunology, gastroenterology and immunotoxicology during a Workshop, organised by the European branch of the International Life Sciences Institute (ILSI Europe), on 'Markers